JP2016054314A - Multimode monolithic vertical cavity surface emitting laser array and laser system including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a monolithic VCSEL array in which VCSELs are configured to emit laser beams at different wavelengths, respectively.SOLUTION: A monolithic surface emitting laser array includes a reflector 104, a light emitting layer 102 and a diffraction grating layer 112 configured to use two or more nonperiodical subwavelength diffraction gratings. Each diffraction grating is configured to form a cavity resonator together with the reflector. Each diffraction grating is configured to use a diffraction grating pattern achieving one or more internal cavity modes and achieving one or more external transverse modes emitted through the diffraction grating.SELECTED DRAWING: Figure 1A

Description

  Various embodiments of the present invention relate to lasers, and more particularly to semiconductor lasers.

  Semiconductor lasers can be used in a wide variety of applications, including displays, solid-state lighting, sensing, printing and telecommunications to name a few, so one of the most important types of lasers currently in use. Is representative. Two types of semiconductor lasers that are mainly used are edge-emitting lasers and surface-emitting lasers. The edge-emitting laser generates light that travels in a direction substantially parallel to the light emitting layer. On the other hand, the surface emitting laser generates light that travels perpendicular to the light emitting layer. A surface emitting laser has several advantages over a normal edge emitting laser. Surface emitting lasers can emit light more efficiently and can be arranged to form a two-dimensional light emitting array.

  A surface emitting laser composed of a light emitting layer sandwiched between two reflectors is called a vertical cavity surface emitting laser (“VCSEL”). The reflector is typically a distributed Bragg reflector ("DBR"), ideally forming a reflective resonator with reflectivity higher than 99% for optical feedback. The DBR is composed of a plurality of alternating layers, and each layer is composed of a dielectric or semiconductor material whose refractive index changes periodically. Two adjacent layers in the DBR have different refractive indices and are called “DBR pairs”. DBR reflectivity and bandwidth depend on the refractive index contrast of the constituent material of each layer and the thickness of each layer. The materials used to form the DBR pair typically have a similar composition and therefore have a relatively small refractive index difference. Therefore, to achieve a resonator reflectivity higher than 99% and to provide a narrow mirror bandwidth, the DBR has about 15 to about 40, or more DBR pairs anywhere. It is comprised so that it may have. However, creating a DBR with a reflectivity higher than 99% proved difficult, especially for VCSELs designed to emit light with wavelengths in the blue-green and long infrared portions of the electromagnetic spectrum. ing.

  Physicists and engineers continue to improve the design, operation and efficiency of VCSELs.

1 is an isometric view of an example monolithic VCSEL array configured in accordance with one or more embodiments of the present invention. FIG. 1B is an exploded isometric view of the monolithic VCSEL array shown in FIG. 1A configured in accordance with one or more embodiments of the present invention. FIG. 1B is a cross-sectional view of a VCSEL array along line AA shown in FIG. 1A, according to one or more embodiments of the invention. FIG. 3 is a plan view of a subwavelength diffraction grating configured using a one-dimensional diffraction grating pattern according to one or more embodiments of the present invention. FIG. 3 is a plan view of a subwavelength diffraction grating configured using a two-dimensional diffraction grating pattern according to one or more embodiments of the invention. FIG. 3 is a plan view of a subwavelength diffraction grating configured using a two-dimensional diffraction grating pattern according to one or more embodiments of the invention. FIG. FIG. 4 is a cross-sectional view of lines from two separate diffraction grating sub-patterns that reveal the phase acquired by reflected light, according to one or more embodiments of the invention. FIG. 6 is a cross-sectional view of lines from two separate grating subpatterns that reveal how the reflected wavefront changes in accordance with one or more embodiments of the present invention. FIG. 6 is an isometric view of an exemplary phase change contour map generated by a diffraction grating pattern configured in accordance with one or more embodiments of the present invention. FIG. 6 is a side view of a subwavelength diffraction grating configured to focus incident light in focus according to one or more embodiments of the invention. FIG. 4 is a plot of reflectivity and phase shift over a range of incident light wavelengths for a subwavelength grating configured in accordance with one or more embodiments of the present invention. FIG. 5 is a diagram illustrating a phase contour plot of phase variation as a function of period and duty cycle obtained in accordance with one or more embodiments of the present invention. 2 is a plan view of a one-dimensional subwavelength diffraction grating configured to operate as a condensing cylindrical mirror, according to one or more embodiments of the invention. FIG. 2 is a plan view of a one-dimensional subwavelength diffraction grating configured to operate as a converging spherical mirror, according to one or more embodiments of the invention. FIG. 11A and 11B are cross-sectional views of VCSEL array cavity resonators operating in accordance with one or more embodiments of the present invention. 3 is an example plot of virtual resonator modes and luminance or gain profiles associated with a VCSEL array configured in accordance with one or more embodiments of the invention. FIG. 6 illustrates a plano-concave resonator that schematically represents a cavity resonator of one VCSEL in a VCSEL array configured in accordance with one or more embodiments of the present invention. FIG. 6 illustrates various ways in which light can be emitted from a VCSEL of a VCSEL array, according to one or more embodiments of the present invention. FIG. 15A is an isometric view of a second example VCSEL array configured in accordance with one or more embodiments of the present invention. FIG. 15B is a cross-sectional view along line BB of a second example VCSEL array configured in accordance with one or more embodiments of the invention. FIG. 16A is an isometric view of a third example VCSEL array configured in accordance with one or more embodiments of the present invention. FIG. 16B is a cross-sectional view along line CC of a third example VCSEL array configured in accordance with one or more embodiments of the present invention. 1 is an isometric view of an example laser system configured in accordance with one or more embodiments of the present invention. FIG.

  Various embodiments of the invention are directed to monolithic VCSEL arrays, where each VCSEL can be configured to lase laser light at a different wavelength. Each VCSEL in the VCSEL array includes one or more flat, non-periodic subwavelength gratings (“SWG”). Each VCSEL SWG can be configured to have a different diffraction grating configuration so that each VCSEL can emit laser light at different wavelengths. The SWG of each VCSEL can be configured to control the shape of the internal resonator mode and the shape of the external mode emitted from the VCSEL. Each VCSEL has a small mode volume, generally a single spatial output mode, and can be configured to emit light over a narrow wavelength range and emit a single polarization of light.

  In the following description, the term “light” refers to electromagnetic radiation having wavelengths in the visible and invisible portions of the electromagnetic spectrum, including the infrared and ultraviolet portions of the electromagnetic spectrum.

  It should also be noted that in the following description, for simplicity and convenience, the VCSEL array embodiments of the present invention are described as having a square array of four VCSELs. However, embodiments of the present invention are not intended to be so limited. A VCSEL array embodiment may actually be configured with any suitable number of VCSELs, and the VCSEL may have any suitable arrangement within the monolithic VCSEL array.

Vertical Cavity Surface Emitting Array FIG. 1A shows an isometric view of an example monolithic VCSEL array 100 configured in accordance with one or more embodiments of the present invention. The VCSEL array 100 includes a light emitting layer 102 disposed on a distributed Bragg reflector (“DBR”) 104. The DBR 104 is further disposed on the substrate 106, and the substrate 106 is disposed on the first electrode 108. The VCSEL array 100 also includes an insulating layer 110 disposed on the light emitting layer 102, a diffraction grating layer 112 disposed on the layer 110, and a second electrode 114 disposed on the diffraction grating layer 112. As shown in the example of FIG. 1A, the second electrode 114 is configured to have four rectangular openings 116 to 119, and each opening exposes a part of the diffraction grating layer 112. As indicated by arrows 120-123, each opening causes the longitudinal or axial mode of light emitted from the light-emitting layer 102 to exit the VCSEL substantially perpendicular to the xy plane of the layer. (Ie, the longitudinal mode of light is emitted from the VCSEL array 100 through each aperture in the z direction).

  FIG. 1B shows an exploded isometric view of a VCSEL array 100 configured in accordance with one or more embodiments of the present invention. The isometric view reveals four openings 126-129 in the insulating layer 110 and four SWGs 132-135 in the diffraction grating layer 112. The openings 126 to 129 allow the light emitted from the light emitting layer 102 to reach the corresponding SWGs 132 to 135, respectively. It should be noted that embodiments of the present invention are not limited to openings 116-119 and 126-129 having rectangular shapes. In other embodiments, the openings in the second electrode and insulating layer can be square, circular, elliptical, or any other suitable shape.

Note that each SWG 116-119 defines a separate VCSEL within the monolithic VCSEL array 100. All four VCSELs defined by SWGs 116-119 share the same DBR 104 and light-emitting layer 102, except that SWGs 116-119 can be configured to emit laser light at different wavelengths. For example, as shown in FIG. 1A, SWGs 116-119 are configured to emit light having wavelengths [lambda] ₁ , [lambda] ₂ , [lambda] _3, and [lambda] ₄ , respectively. As will be described in more detail later, each SWG can be configured to emit light having a different polarization or to emit unpolarized light.

Layers 104, 106 and 112 are composed of various combinations of suitable compound semiconductor materials. The compound semiconductor includes a group III-V compound semiconductor and a group II-VI compound semiconductor. III-V compound semiconductors are boron (“B”) in combination with a row Va element selected from nitrogen (“N”), phosphorus (“P”), arsenic (“As”) and antimony (“Sb”). ”), Aluminum (“ Al ”), gallium (“ Ga ”) and indium (“ In ”). Group III-V compound semiconductors are classified according to the relative amounts of element III and element V, such as binary compound semiconductors, ternary compound semiconductors, and quaternary compound semiconductors. For example, binary semiconductor compounds include, but are not limited to, GaAs, GaAl, InP, InAs, and GaP. Ternary compound semiconductors include, but are not limited to, In _y Ga _y-1 As or GaAs _y P _1-y . However, y is in the range of 0-1. Four yuan compound semiconductors, but are not limited _to, an _{In x Ga 1-x As y} P 1-y. However, both x and y are independently in the range of 0-1. Group II-VI compound semiconductors are zinc (“Zn”), cadmium (“Cd”) in combination with a VIa element selected from oxygen (“O”), sulfur (“S”) and selenium (“Se”). , Composed of elements of column IIb selected from mercury (“Hg”). For example, suitable II-VI compound semiconductors include, but are not limited to, CdSe, ZnSe, ZnS, and ZnO, which are examples of binary II-VI compound semiconductors.

  The layers of the VCSEL array 100 can be formed using chemical vapor deposition, physical vapor deposition, or wafer bonding. The SWGs 132-135 can be formed in the diffraction grating layer 112 using reactive ion etching, focused beam milling, or nanoimprint lithography, and the diffraction grating layer 112 can be coupled to the insulating layer 110.

  In some embodiments, layers 104 and 106 are doped with p-type impurities, while layer 112 is doped with n-type impurities. In other embodiments, layers 104 and 106 are doped with n-type impurities, while layer 112 is doped with p-type impurities. A p-type impurity is an atom that is incorporated into a semiconductor lattice and introduces empty electron energy levels called “holes” into the electronic band gap of the layer. These dopants are also called “electron acceptors”. On the other hand, n-type impurities are atoms that are incorporated into the semiconductor lattice and introduce electron energy levels that fill the electron band gap of the layer. These dopants are also called “electron donors”. In III-V compound semiconductors, column VI elements replace column V atoms in the III-V lattice and serve as n-type dopants, column II elements replace column III atoms in the III-V lattice, p Serves as a type dopant.

The insulating layer 110 can be composed of an insulating material, such as SiO ₂ or Al ₂ O ₃ or another suitable material having a large electron band gap. Electrodes 108 and 114 may be comprised of suitable conductors such as gold (“Au”), silver (“Ag”), copper (“Cu”), or platinum (“Pt”).

  FIG. 2 shows a cross-sectional view of the VCSEL array 100 along line AA shown in FIG. 1A, according to one or more embodiments of the invention. Its cross-sectional view reveals a structure consisting of individual layers. The DBR 104 is composed of a stack of DBR pairs oriented in parallel to the light emitting layer 102. In practice, the DBR 104 may be composed of about 15 to about 40 or more DBR pairs. An enlarged view 202 of the sample portion of DBR 104 reveals that the layers of DBR 104 have thicknesses of about λ / 4n and λ4n ′, respectively. Where λ is the vacuum wavelength of light emitted from the light emitting layer 102, n is the refractive index of the DBR layer 206, and n ′ is the refractive index of the DBR layer 204. The dark shaded layer 204 represents a DBR layer composed of a first semiconductor material, the thin shaded layer 206 represents a DBR layer composed of a second semiconductor material, and layers 204 and 206 are related. Different refractive indexes. For example, layer 204 can be composed of GaAs and have an approximate refractive index of 3.6, layer 206 can be composed of AlAs and have an approximate refractive index of 2.9, The layer 106 can be composed of GaAs or AlAs.

FIG. 2 also includes an enlarged view 208 of the light emitting layer 102 and reveals one or more possible configurations for the layers that make up the light emitting layer 102. The enlarged view 208 reveals that the emissive layer 102 is composed of three separate quantum well layers (“QW”) 210 separated by a barrier layer 212. QW 210 is disposed between confinement layers 214. The material constituting the QW 210 has a smaller electronic band gap than the barrier layer 212 and the confinement layer 214. The thickness of the confinement layer 214 can be selected so that the total thickness of the light emitting layer 102 is approximately the wavelength of light emitted from the light emitting layer 102. Layers 210, 212 and 214 are composed of different intrinsic semiconductor materials. For example, the QW layer 210 can be made of InGaAs (for example, In _0.2 Ga _0.8 As), the barrier layer 212 can be made of GaAs, and the confinement layer can be made of GaAlAs. . Embodiments of the present invention are not limited to the light emitting layer 102 having three QWs. In other embodiments, the emissive layer can have one, two, or four or more QWs.

FIG. 2 also reveals the configuration of the diffraction grating layer 112. The SWGs 132 and 133 are thinner than the rest of the diffraction grating layer 112 and are suspended above the light emitting layer 102 to create gaps 216 and 217 between the SWGs 132 and 133 and the light emitting layer 102. ) As shown in FIGS. 2 and 1B, SWGs 132-135 can be attached to the diffraction grating layer 112 along one edge, and the air gap separates the three remaining edges of SWGs 132-135 from the diffraction grating layer 112. doing. For example, as shown in FIG. 2, the gap 216 separates the SWG 132 from the diffraction grating layer 112, and the gap 220 separates the SWG 133 from the diffraction grating layer 112. Further, the diffraction grating layer 112 and the insulating layer 110 are configured such that the portion 222 of the diffraction grating layer 112 is in contact with the light emitting layer 102 through the opening of the insulating layer 110. The insulating layer 110 suppresses the flow of current through the portion 222 of the diffraction grating layer 112. The SWGs 132 to 135 and the DBR 104 are reflectors that form a reflective resonator for optical feedback while each VCSEL of the VCSEL array 100 emits laser light. For example, SWG 132 and DBR 104 form an optical resonator of the first VCSEL of VCSEL array 100, and SWG 133 and DBR 104 form an optical resonator of the second VCSEL of VCSEL array 100. SWGs 134 and 135 also form separate optical resonators from DBR 104, that is, optical resonators associated with the third and fourth VCSELs of VCSEL array 100.

Aperiodic Subwavelength Grating As described above, the SWGs 132 to 135 of the diffraction grating layer 112 are mounted as a planar film supported in a floating state above the light emitting layer 102. A SWG configured in accordance with one or more embodiments of the present invention can control the shape of the wavefront of the light reflected back into the corresponding resonator of the VCSEL array 100 and, as shown in FIG. Provides a reflective function, including control of the shape of the wavefront of light emitted through the corresponding openings in the two electrodes 114. This is accomplished by configuring each SWG to have an aperiodic subwavelength grating pattern that controls the phase of light reflected from the SWG without substantially affecting the high reflectivity of the SWG. be able to. As will be shown later, in some embodiments, the SWG can be configured to have a diffraction grating pattern that allows the SWG to operate as a cylindrical or spherical mirror.

  Note that for simplicity, the following description describes configuring only one SWG of the grating layer. In practice, the diffraction grating layer can actually contain a large number of SWGs, and each SWG of the diffraction grating layer can be configured as described later.

FIG. 3A shows a plan view of a SWG 300 configured with a one-dimensional diffraction grating pattern formed in the diffraction grating layer subpattern 302, according to one or more embodiments of the invention. The one-dimensional diffraction grating pattern is composed of a plurality of one-dimensional diffraction grating subpatterns. In the example of FIG. 3A, three diffraction grating sub-patterns 301 to 303 are enlarged. In the embodiment depicted in FIG. 3A, each diffraction grating sub-pattern is a plurality of regularly spaced materials of diffraction grating layer 102 material, referred to as “lines”, formed in the diffraction grating layer 302. Including a wire-like portion. The lines extend in the y direction and are periodically spaced in the x direction. FIG. 3A also includes an enlarged end view 304 of the diffraction grating subpattern 302. Lines 306 are separated by grooves 308. Each sub-pattern can be characterized by a specific periodic line spacing and a line width in the x direction. For example, sub-pattern 301 includes lines with width w ₁ separated by period p ₁ , sub-pattern 302 includes lines with width w ₂ separated by period p ₂ , and sub-pattern 303 has period p ₃ only containing the separated line of width w _3.

ただし、ｗはライン幅であり、ｐはラインの周期間隔である。 Diffraction grating subpattern 301 to 303, to form a sub-wavelength diffraction grating, the diffraction grating, with the proviso that period _p 1, _{p 2} and _{p 3} are smaller than the wavelength of the incident light, one direction, ie, x Preferentially reflects incident light polarized in the direction. For example, depending on the wavelength of the incident light, the line width can be in the range of about 10 nm to about 300 nm, and the period is about 20 nm to about 1 nm.
It can be in the range of μm. The light reflected from a certain area acquires a phase φ determined by the line thickness t and a duty cycle η defined as follows.

However, w is a line width and p is a period interval of a line.

  The SWG 300 can be configured to add a specific phase change to the reflected light while maintaining a very high reflectivity. The one-dimensional SWG 300 can be configured to reflect the x-polarized component or the y-polarized component of incident light by adjusting the line period, line width, and line thickness. For example, a specific period, line width, and line thickness may be suitable because it reflects the x-polarized component but not the y-polarized component, and reflects the y-polarized component but not the x-polarized component. Thus, different periods, line widths and line thicknesses may be suitable.

  Embodiments of the present invention are not limited to one-dimensional diffraction gratings. The SWG can be configured to have a two-dimensional aperiodic diffraction grating pattern in order to reflect the polarity insensitive light. 3B-3C illustrate plan views of two flat SWG examples having a two-dimensional aperiodic subwavelength grating pattern, according to one or more embodiments of the present invention. In the example of FIG. 3B, the SWG is constituted by a post, not a line separated by a groove. The duty cycle and period can be varied in the x and y directions. Enlarged views 310 and 312 show plan views of two different rectangular post sizes. FIG. 3B includes an isometric view 314 of the posts that make up the enlarged view 310. Embodiments of the present invention are not limited to rectangular posts; in other embodiments, the posts can be square, circular, elliptical or any other suitable shape. In the example of FIG. 3C, the SWG is configured as a hole rather than a post. Enlarged views 316 and 318 show two different rectangular hole sizes. The duty cycle can be changed in the x and y directions. FIG. 3C includes an isometric view 320 that constitutes an enlarged view 316. Although the holes shown in FIG. 3C are rectangular, in other embodiments, the holes can be square, circular, elliptical, or any other suitable shape.

  In other embodiments, the line spacing, thickness, and period can be continuously varied in both one-dimensional and two-dimensional diffraction grating patterns.

Each diffraction grating sub-pattern 301-303 of SWG 300 reflects incident light polarized in one direction, eg, the x-direction, differently due to the different duty cycles and periods associated with each sub-pattern. . FIG. 4 shows a cross-sectional view of lines from two separate grating subpatterns that reveal the phase acquired by reflected light, according to one or more embodiments of the invention. For example, lines 402 and 403 can be lines in a first diffraction grating sub-pattern located in SWG 400, and lines 404 and 405 are second diffractions located elsewhere in SWG 400. It can be a line in a lattice sub-pattern. The thickness t ₁ of lines 402 and 403 is thicker than the thickness t ₂ of lines 404 and 405, and the duty cycle η ₁ associated with lines 402 and 403 is also greater than the duty cycle η ₂ associated with lines 404 and 405. Light that is polarized in the x direction and incident on lines 402-405 becomes confined by lines 402 and 403 for a relatively longer time than the portion of incident light that is confined by lines 404 and 405. As a result, the portion of light reflected from lines 402 and 403 acquires a greater phase shift than the portion of light reflected from lines 404 and 405. As shown in the example of FIG. 4, incident waves 408 and 410 strike lines 402-405 with approximately the same phase, but wave 412 reflected from lines 402 and 403 is a wave reflected from lines 404 and 405. A phase shift φ that is relatively larger than the phase φ ′ acquired by 414 is acquired (ie, φ> φ ′).

FIG. 5 illustrates a cross-sectional view of lines 402-405 that reveal how the reflected wavefront changes, according to one or more embodiments of the invention. As shown in the example of FIG. 5, incident light having a substantially uniform wavefront 502 impinges on lines 402-405, producing reflected light having a curved reflected wavefront 504. The curved reflected wavefront 504 is the portion where the incident wavefront 502 interacts with lines 402 and 403 having a relatively large duty cycle η ₁ and thickness t ₁ , and the same incident wavefront 502 has a relatively small duty cycle η ₂ and due to partial to interact with lines 404 and 405 having a thickness _{t 2.} The shape of the reflected wavefront 504 matches the large phase acquired by the light impinging on the lines 402 and 403 with respect to the small phase acquired by the light impinging on the lines 404 and 405.

FIG. 6 shows an isometric view of an exemplary phase change contour diagram 600 generated by a particular grating pattern of SWG 602, according to one or more embodiments of the present invention. The contour map 600 represents the magnitude of the phase change acquired by the light reflected from the SWG 602. In the example shown in FIG. 6, the diffraction grating pattern of the SWG 602 has the largest phase magnitude acquired by the light reflected near the center of the SWG 602, and the phase acquired by the reflected light when separated from the center of the SWG 602. A contour map 602 is generated in which the size of is reduced. For example, the reflected light acquires phi ₁ phase from sub-patterns 604, light reflected from the sub-pattern 606 acquires phi ₂ phase. Since φ ₁ is much larger than φ _2, the light reflected from sub-pattern 606 acquires a much larger phase than the light reflected from sub-pattern 608.

  The phase change further shapes the wavefront of the light reflected from the SWG. For example, as described above with reference to FIGS. 4 and 5, a line having a relatively large duty cycle has a larger phase shift in reflected light than a line having a relatively small duty cycle. cause. As a result, the first portion of the wavefront reflected from the line having the first duty cycle is the same wavefront reflected from a different set of lines configured to have a relatively small second duty cycle. Be late to the second part of Embodiments of the present invention form a SWG pattern to change the phase and ultimately the reflected wavefront so that the SWG can operate as a mirror with specific optical properties, such as a collection mirror. Including controlling the shape.

  FIG. 7 illustrates a side view of a SWG 702 configured to operate as a collector mirror according to one or more embodiments of the present invention. In the example of FIG. 7, the SWG 702 is configured using a diffraction grating pattern in which incident light polarized in the x direction is reflected and its wavefront corresponds to focusing the reflected light at the focal point 704.

ただし、Ｒ（λ）はＳＷＧの反射率であり、φ（λ）はＳＷＧによって引き起こされる位相シフト又は位相変化である。図８は、本発明の１つ以上の実施形態による、一例のＳＷＧのための入射光波長の範囲にわたる反射率及び位相シフトのプロットを示す。この例では、回折格子層は、１次元回折格子を有するように構成され、回折格子層のラインに対して垂直に偏光された電界成分を有する垂直入射において動作する。図８の例では、約１．２μｍから約２．０μｍの波長範囲にわたる入射光の場合に、曲線８０２は反射率Ｒ（λ）に対応し、曲線８０４はＳＷＧによって引き起こされる位相シフトφ（λ）に対応する。反射率及び位相曲線８０２及び８０４は、既知の有限要素法、又は厳密結合波解析のいずれかを用いて求めることができる。ＳＷＧ及び空気の屈折率コントラストが強いことに起因して、ＳＷＧは、高い反射率８０６の広いスペクトル領域を有する。しかしながら、曲線８０４は、反射光の位相が、破線８０８と８１０との間の高反射率のスペクトル領域全体にわたって変動することを明らかにする。 Configuring Aperiodic Subwavelength Gratings Embodiments of the present invention include several methods that can be configured to operate each SWG of the grating layer as a mirror. A first method for configuring a SWG to reflect light having a desired wavefront includes determining a reflection coefficient profile for the SWG grating layer. The reflection coefficient is a complex value function represented by the following equation.

Where R (λ) is the SWG reflectivity and φ (λ) is the phase shift or phase change caused by the SWG. FIG. 8 shows a plot of reflectivity and phase shift over a range of incident light wavelengths for an example SWG, according to one or more embodiments of the invention. In this example, the diffraction grating layer is configured to have a one-dimensional diffraction grating and operates at normal incidence with the electric field component polarized perpendicular to the lines of the diffraction grating layer. In the example of FIG. 8, for incident light over a wavelength range of about 1.2 μm to about 2.0 μm, curve 802 corresponds to reflectivity R (λ) and curve 804 is the phase shift φ (λ ). The reflectivity and phase curves 802 and 804 can be determined using either known finite element methods or exact coupled wave analysis. Due to the strong refractive index contrast of SWG and air, SWG has a wide spectral region with high reflectivity 806. However, curve 804 reveals that the phase of the reflected light varies across the high reflectance spectral region between dashed lines 808 and 810.

When the spatial dimension of the line period and width is uniformly changed by the factor α, the reflection coefficient profile is not substantially changed, but the wavelength axis is scaled by the factor α. In other words, when the diffraction grating is designed to have a specific reflection coefficient R ₀ at free space wavelength λ ₀ , the new diffraction grating with the same reflection coefficient at different wavelengths λ will have a period, line thickness and line width. Can be designed by multiplying all diffraction grating geometric parameters such as by a factor α = λ / λ ₀ to give r (λ) = r ₀ (λ / α) = r ₀ (λ ₀ ).

In addition, by scaling the original periodic grating parameters non-uniformly within the high reflectance spectral window 806, | R (λ) | → 1, but diffracting so that the phase varies spatially. A grid can be designed. Assume that it is desired to introduce the phase φ (x, y) into the portion of light reflected from a point on the SWG using the lateral coordinates (x, y). Whether the non-uniform diffraction grating having a gradually changing diffraction grating scale factor α (x, y) is a periodic diffraction grating having a reflection coefficient R ₀ (λ / α) near the point (x, y). It behaves locally like Thus, given a periodic grating design with phase φ ₀ at a certain wavelength λ ₀ , φ (x at the operating wavelength λ can be selected by selecting a local scale factor α (x, y) = λ / λ _0. , Y) = φ ₀ is given. For example, in a SWG design, it is desirable to introduce a phase of about 3π into a portion of the light reflected from a point (x, y), but the line width and period selected for that point (x, y) Suppose that introduces a phase of about π. Referring back to the plot of FIG. 8, the desired phase φ ₀ = 3π corresponds to the point 812 on the curve 804 and the wavelength λ ₀ ≈1.67 μm 814, and the phase π associated with the point (x, y) is the curve 804. This corresponds to the upper point 816 and the wavelength λ≈1.34 μm. Therefore, the scale factor is α (x, y) = λ / λ ₀ = 1.34 / 1.67 = 0.802, and in order to obtain the desired phase φ ₀ = 3π at the operating wavelength λ = 1.34 μm. , The line width and period at the point (x, y) can be adjusted by multiplying by a factor α.

The plot of reflectivity and phase shift versus wavelength range shown in FIG. 8 shows the SWG parameters such as line width, line thickness and period to introduce a specific phase into the light reflected from a specific point on the SWG. Represents one way that can be determined. In other embodiments, phase variations as a function of period and duty cycle can be used to configure the SWG. FIG. 9 shows a phase contour plot of phase variation as a function of period and duty cycle that can be used to construct a SWG according to one or more embodiments of the present invention. The contour plot shown in FIG. 9 can be generated using either known finite element methods or exact coupled wave analysis. Each contour line, such as contour lines 901-903, corresponds to a particular phase acquired by light reflected from a diffraction grating pattern having a certain period and duty cycle located anywhere along the contour line. Their phase contours are separated by 0.25π rad. For example, the contour line 901 is -0.
The contour line 902 corresponds to the period and duty cycle for adding a phase of −0.5π rad to the reflected light. A phase between −0.25π rad and −0.5π rad is added to the light reflected from the SWG with period and duty cycle located between the contour lines 901 and 902. A first point (p, η) 904 corresponding to a grating period of 700 nm and a duty cycle of 54%, and a second point (p, η) 906 corresponding to a grating period of 660 nm and a duty cycle of 60% Are located on the contour line 901 and cause the same phase shift -0.25π, but with different duty cycles and line period spacing.

  FIG. 9 also includes two reflectance contour lines that overlap on the phase contour surface for 95% and 98% reflectance, respectively. Dashed contour lines 908 and 910 correspond to 95% reflectivity, and solid contour lines 912 and 914 correspond to 98% reflectivity. A point (p, η, φ) located anywhere between contour lines 908 and 910 has a minimum reflectance of 95% and is located anywhere between contour lines 912 and 914 (P, η, φ) has a minimum reflectance of 98%.

  A grating that can operate as a specific type of mirror with minimal reflectivity, using the points (p, η, φ) represented by the phase contour plot, as described below in the next subsection. The period and duty cycle for can be selected. In other words, the SWG optical device can be designed using the data represented in the phase contour plot of FIG. In some embodiments, the SWG can be designed and fabricated with a fixed period or duty cycle, while changing other parameters. In other embodiments, both the period and duty cycle can be changed to design and make the SWG.

  In some embodiments, the SWG of the grating layer can be configured to operate as a cylindrical mirror having a constant period and a variable duty cycle. FIG. 10A is configured to operate as a condensing cylindrical mirror for incident light formed in the grating layer 1002 and polarized parallel to the x-direction, according to one or more embodiments of the present invention. A plan view of the one-dimensional SWG 1000 is shown. FIG. 10A includes shaded areas such as shaded areas 1004-1007, where each shaded area represents a different duty cycle, and a dark shaded area such as area 1004 is a thin mesh such as area 1007. It represents a region having a duty cycle that is relatively larger than the multiplying region. FIG. 10A also includes magnified views 1010-1012 of the sub-regions, which show that the lines are parallel in the y direction and the line period interval p is constant or fixed in the x direction. Make it clear. Enlargements 1010-1012 also reveal that the duty cycle η decreases as it moves away from the center. The SWG 1000 is configured to focus the reflected light polarized in the x direction, as described above with reference to FIG. FIG. 10A also includes examples of isometric view 1008 and plan view 1010 which are contour plots of the reflected beam profile at the focal point. The V axis 1012 is parallel to the y direction and represents the vertical component of the reflected beam, and the H axis 1014 is parallel to the x direction and represents the horizontal component of the reflected beam. When the reflected beam profiles 1008 and 1010 are incident light polarized in the x direction, the SWG 1000 is narrow in the direction perpendicular to the line (“H” or x direction) and parallel to the line (“V 'Or y direction) to reflect a wide Gaussian beam.

In one embodiment, a SWG having a constant period can be configured to operate as a spherical mirror for incident polarization by tapering the lines of the grating layer away from the center of the SWG. FIG. 10B illustrates a one-dimensional SWG 1020 formed in the grating layer 1022 and configured to operate as a converging spherical mirror for incident light polarized in the x direction, according to one or more embodiments of the invention. A plan view is shown. The SWG 1020 defines a circular mirror diameter. The diffraction grating pattern of SWG 1020 is represented by annular shaded areas 1024 to 1027. Each shaded annular region represents a different diffraction grating sub-pattern of lines. Enlargements 1030-1033 reveal that the lines are tapered in the y direction and have a constant line period spacing p in the x direction. Specifically, enlarged views 1030-1032 are enlarged views of the same line extending parallel to the dashed reference line 1036 in the y direction. Enlarged views 1030-1032 show that the period p is fixed. Each annular region has the same duty cycle η. For example, enlarged views 1031-1033 include portions of different lines within annular region 1026 having substantially the same duty cycle. As a result, each portion of the annular region imparts approximately the same phase shift to the light reflected from the annular region. For example, light reflected from any location within the annular region 1026 acquires substantially the same phase shift φ. FIG. 10B also includes examples of an isometric view 1038 and a plan view 1039 that are contour plots of the reflected beam profile at the focal point. Beam profiles 1038 and 1039 reveal that spherical SWG 1020 produces a symmetric Gaussian reflected beam that is narrower in the V or x direction than the reflected beam of SWG 1000.

  SWGs 1000 and 1020 represent only two or many different types of SWGs of diffraction grating layers that can be configured in accordance with one or more embodiments of the present invention. Each SWG of the diffraction grating layer can be configured to have different reflection characteristics.

Laser Operation and Resonator Configuration Since each VCSEL in the VCSEL array operates in the same way, the operation of only one VCSEL in the VCSEL array 100 will be described. 11A and 11B show cross-sectional views of one cavity resonator of a VCSEL array 100 that operates in accordance with one or more embodiments of the present invention. As shown in FIG. 11A, electrodes 114 and 108 are electronically coupled to a voltage source 1102 that is used to electronically pump light emitting layer 102. FIG. 11A includes an enlarged view 1104 of a part of SWG 1106, a gap 1108, a part of light emitting layer 102, and a part of DBR 104. SWG 1106 represents one of SWGs 132-135. When the VCSEL array 100 is unbiased, the QW 210 will have a relatively low concentration of electrons in the corresponding conduction band and a relatively low concentration of free electron states in the corresponding valence band, ie, holes. The light emitting layer 102 hardly emits light. On the other hand, when a forward bias is applied to the layers of the VCSEL array 100, electrons are injected into the conduction band of the QW 210, while holes are injected into the valence band of the QW 210, and in a process called inversion distribution, New conduction band electrons and excess valence band holes. In a radiation process called “electron-hole recombination” or “recombination”, electrons in the conduction band spontaneously recombine with holes in the valence band. When electrons and holes recombine, light is first emitted in all directions over a range of wavelengths. In the forward bias direction, as long as an appropriate operating voltage is applied, the electron and hole inversion distribution is maintained in the QW 210, and the electrons spontaneously recombine with the holes and emit light in almost all directions. it can.

As described above, SWG 1106 and DBR 104 reflect light emitted over a narrow wavelength range substantially perpendicular to light emitting layer 102 back into light emitting layer 102, as indicated by arrow 1108. It can be configured to form a resonator. The light reflected back into QW 210 induces further light emission from QW 210 in a chain reaction. Note that the emissive layer 102 initially emits light over a range of wavelengths by spontaneous emission, but SWG 1106 selects and reflects the wavelength λ _i back into the emissive layer 102, causing stimulated emission. I want. However, i is equal to 1, 2, 3 or 4. This wavelength is called longitudinal mode, axial mode, or z-axis mode. Over time, the gain becomes saturated by the longitudinal mode, the longitudinal mode begins to dominate the light emission from the light-emitting layer 102, and the other longitudinal modes disappear. In other words, the light that reflects between SWG 1106 and DBR 104 and does not reciprocate leaks out of VCSEL array 100 without appreciably being amplified as the longitudinal mode supported by the resonator begins to dominate, Eventually disappears. As shown in FIG. 11B, the dominant longitudinal mode reflected between the SWG 1106 and the DBR 104 is amplified as it travels back and forth across the emissive layer 102 to generate a standing wave 1110 and its standing The wave terminates in SWG 1106 and extends into DBR 104. Eventually, from SWG 1106, a substantially coherent light beam 1112 having wavelength λ _i emerges. The light emitted from the light emitting layer 102 enters the DBR 104 and the SWG 1106 and adds a contribution to the round trip phase of the light in the resonator. DBR 104 and SWG 1106 can be thought of as perfect mirrors that shift space to provide an effective additional phase shift.

Each SWG of the VCSEL array can be configured to select different longitudinal mode light emitted from the light emitting layer 102. FIG. 12 shows an example plot 1202 of the brightness or gain profile 1204 of light emitted from the light emitting layer 102 about the wavelength λ, according to one or more embodiments of the invention. FIG. 12 includes an example plot 1206 of four different single resonator modes, where each single resonator mode is associated with a VCSEL array 100 of different VCSELs. For example, the peaks in plot 1206 represent single longitudinal resonator modes λ ₁ , λ ₂ , λ _3, and λ ₄ , which are associated with the four resonators formed by SWGs 132-135 and DBR 104, respectively. The emissive layer 102 radiates and utilizes a wide range of wavelengths represented by the luminance profile 1204, and the resonator associated with each VCSEL indicates from the profile the longitudinal single resonator mode represented in plot 1206. Select one of them. Each longitudinal mode is amplified in the resonator of the associated VCSEL and emitted as described above with reference to FIG. For example, plot 1208 shows the luminance profile of the wavelengths emitted from the four VCSELs of VCSEL array 100. As shown in plot 1208, each longitudinal mode can radiate with substantially the same brightness.

  Note that although VCSEL arrays are shown to emit different wavelengths for each VCSEL, embodiments of the present invention are not intended to be so limited. In other embodiments, any combination of VCSELs, including all VCSELs in a VCSEL array, can be configured to emit the same wavelength.

  As described above in the preceding subsection “Constructing an Aperiodic Subwavelength Grating”, each SWG of the grating layer implements an internal longitudinal resonator mode or an internal z-axis resonator mode, It can be configured to operate as a concave mirror. FIG. 13 illustrates a plano-concave resonator 1302 that schematically represents a VCSEL cavity resonator configuration within the VCSEL array 100, according to one or more embodiments of the present invention. The plano-concave resonator 1302 includes a plane mirror 1304 and a concave mirror 1306. The DBR 104 of the VCSEL array 100 corresponds to the plane mirror 1304, and the SWG 1106 operates as a concave mirror that reflects light so that the light is concentrated in the region of the light emitting layer 102 between the SWG 1106 and the DBR 104 as described above. Can be configured. For example, the SWG 1106 can be configured to reflect light of the luminance profile represented in FIGS. 10A and 10B.

Each VCSEL in the VCSEL array can be configured to emit a different polarization resonator mode. For example, some VCSELs can be configured to emit light polarized in various directions, while other VCSELs can be configured to emit unpolarized light. As described above in the preceding subsection “Constructing an Aperiodic Subwavelength Grating”, the SWG is reflected to reflect light polarized substantially perpendicular to the SWG lines and grooves. Can be configured. In other words, the SWG of the cavity resonator selects a component having a specific polarization from the light emitted from the light emitting layer. The polarization component of the light emitted from the light emitting layer is selected by the SWG and reflected back into the resonator. When the gain is saturated, only the longitudinal mode with the polarization selected by the SWG is amplified. Longitudinal modes emitted from the emissive layer not selected by the SWG leak out of the VCSEL array 100 without appreciably being amplified. In other words, a mode having a polarization other than the polarization selected by the SWG disappears and is not amplified by the resonator. Eventually, only modes polarized in the direction selected by the SWG are emitted from the VCSEL array.

  FIG. 14 illustrates an example of polarized light emitted from one VCSEL of the VCSEL array 100, according to one or more embodiments of the invention. The light emitted from the light emitting layer 102 is not polarized. However, one polarization state is selected by the SWG 132 as the gain saturates over time. A double arrow 1402 incident on the SWG 132 from within the VCSEL array 100 represents the polarization state selected by the SWG 132. As described above, the SWG 132 can be configured to have lines and grooves extending in parallel to the y direction. In the example of FIG. 14, the SWG 132 selects only the longitudinal mode emitted from the light emitting layer 102 that is polarized in the x direction. The polarized light is amplified in the resonator formed by SWG 132 and DBR 104 as described above with reference to FIG. As shown in the example of FIG. 14, the light emitted through SWG 132 is polarized in the x direction, as represented by a double arrow 1404.

In addition to supporting a particular longitudinal or axial mode of vibration, corresponding to standing waves supported by the resonator along the z-direction, a transverse mode can also be supported by each resonator. The transverse mode is perpendicular to the resonator or z-axis and is known as the TEM _nm mode. However, the subscripts m and n are integers of horizontal nodal lines in the x and y directions across the appearing beam. In other words, the beam formed in the resonator can be divided into one or more regions in its cross section. The SWG can be configured to support only one or a specific transverse mode.

FIG. 14 also illustrates an example of two transverse modes generated in the resonator 1406 formed by the SWG 1408 and the DBR 104, according to one or more embodiments of the present invention. The SWG 1408 can represent any one of the SWGs 132 to 135. As described above, the SWG 1408 can be configured to define the size of the resonator. As shown in FIG. 14, the TEM ₀₀ mode is represented by a dashed curve 1410 and the TEM ₁₀ mode is represented by a solid curve 1412. The TEM ₀₀ mode has no nodes and is entirely within the resonator 1406. On the other hand, the TEM ₁₀ mode has one node in the x direction, and the portions 1414 and 1416 exist outside the resonator 1406. As a result, during gain saturation, the TEM ₀₀ mode is amplified because it is completely present in resonator 1406. However, since a portion of the TEM ₁₀ mode exists outside the resonator 1406, the TEM ₁₀ mode decreases and eventually disappears during gain saturation, but the TEM ₀₀ mode continues to amplify. Other TEM _mn modes that cannot be supported by the resonator 1406 or that cannot be completely present in the resonator 1406 are also extinguished.

FIG. 14 shows a contour plot 1418 of the luminance profile of TEM ₀₀ emitted from one VCSEL of the VCSEL array 100, according to one or more embodiments of the invention. TEM ₀₀ emerges from SWG 133 to have a substantially flat coherent wavefront and have a Gaussian transverse irradiance profile represented by contour plot 1418. The luminance profile is symmetric about the z axis. The external TEM ₀₀ mode corresponds to the internal TEM ₀₀ mode and can be generated by the SWG 133 configured to operate as a spherical mirror as described above with reference to FIG. 10B. In other embodiments, the SWG 133 is narrow in the direction perpendicular to the SWG 133 line (x direction) and parallel to the SWG 133 line (y) as described above with reference to FIG. 10A. Can be configured to operate as a cylindrical mirror that produces a wide lowest order transverse mode TEM ₀₀ in the direction). By placing the fiber so that the core of the fiber is located very close to the SWG 133, the TEM ₀₀ mode can be coupled to the core of the optical fiber. The SWG 133 can also be configured to emit a transverse mode suitable for coupling into the hollow waveguide, such as the EH ₁₁ mode of the hollow waveguide.

  The SWG can be configured to generate a light beam having a specific brightness profile pattern. FIG. 14 shows a cross-sectional view 1420 of an example of a light beam emitted from a VCSEL. Cross-sectional view 1420 reveals a light beam having a donut-shaped luminance profile along the length of the beam. The intensity profile of the radiation beam along line 1414 reveals a cylindrical beam. The SWG can also be configured to generate other types of cross-sectional beam patterns, such as Airy beam or Bessel beam profiles.

  Returning to FIGS. 1 and 2, the insulating layer 110 is configured to provide current and light confinement. However, as described above with reference to FIG. 13, the SWG can be configured to confine the reflected light in the region of the light emitting layer located between the SWG and the DBR, so that the VCSEL of the present invention. The array embodiment is not limited to including the insulating layer 110. 15A and 15B show an isometric view and a cross-sectional view along line BB of an example VCSEL array 1500 configured in accordance with one or more embodiments of the present invention. The VCSEL array 1500 is similar to the VCSEL array 100 except that the insulating layer 110 of the VCSEL array 100 is not present in the VCSEL array 1500. Instead, each SWG of the diffraction grating layer 112 is configured to guide reflected light into the region of the light emitting layer 102 located between the SWG and the DBR 104.

  Note that the height and resonator length of a VCSEL configured in accordance with embodiments of the present invention is significantly shorter than the height and resonator length of a conventional VCSEL configured with two DBRs. For example, a typical VCSEL DBR has about 15 to about 40 DBR pairs, corresponding to about 5 μm to about 6 μm, anywhere, while SWG ranges from about 0.2 μm to about 0.3 μm. It has a thickness and has an equivalent or higher reflectivity.

  In yet another embodiment of the invention, the height of the VCSEL array can be further reduced by using two grating layers. 16A and 16B illustrate an isometric view and a cross-sectional view along line CC of an example VCSEL array 1600 configured in accordance with one or more embodiments of the present invention. The VCSEL array 1600 is similar to the VCSEL array 100 except that the DBR 104 is replaced with a second diffraction grating layer 1602. As shown in FIG. 16B, the SWGs of the diffraction grating layers 112 and 1602 are aligned to form a cavity resonator. For example, SWGs 132 and 1604 form a cavity resonator. The SWG of the diffraction grating layer 1602 has a one-dimensional or two-dimensional diffraction grating pattern, and can be configured to operate in the same manner as the SWG of the diffraction grating layer 112 described above. Since the SWG pair of the diffraction grating layer operates as a spherical resonator and can be configured to guide the reflected light into the region of the light emitting layer 102, the insulating layer 110 may be unnecessary.

Embodiments of the present invention include a laser system for propagating the wavelength of light output from each VCSEL of a VCSEL array into a waveguide. FIG. 17 illustrates an isometric view of an example laser system 1700 configured in accordance with one or more embodiments of the present invention. The system 1700 includes a monolithic VCSEL array 1701 that includes seven VCSELs 1702-1708 and a multiple waveguide fiber 1710 that includes seven waveguides 1712-1718. As shown in the example of FIG. 17, the seven VCSELs 1702-1708 are arranged to match the configuration of the waveguides 1712-1718, and the light emitted from each VCSEL is guided by the waveguides as indicated by the arrows. Allow direct bonding inside. For example, the waveguide can be a single mode core of optical fiber, and VCSEL1
702-1708 can be configured to output a single mode, such as TEM ₀₀ , as described above with reference to FIG. 14 that couples directly to the corresponding core.

  In certain embodiments, the fiber 1710 can be a photonic crystal fiber. FIG. 17 includes a plan view of a photonic crystal fiber 1712 that includes seven cores 1714. Each core is surrounded by a hollow tube 1715 that spans the length of the fiber. The hollow tube 1715 serves as a cladding layer that confines light in the higher order refractive index core 1714. The VCSEL array 1701 can be configured such that the VCSELs 1702-1708 are aligned with the core 1714 of the fiber 1712 to couple light into the core of the fiber 1712.

  In other embodiments, rather than using photonic crystal fibers to carry the light produced by the VCSEL array, the VCSEL outputs a mode of light that matches the mode supported by the hollow waveguide. A group of hollow waveguides can also be used, provided that they are configured.

  In order to provide a thorough understanding of the present invention, specific explanations have been used in the foregoing description for convenience of description. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the invention. The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. These embodiments are not intended to be exhaustive or to limit the invention to the precise form disclosed. Obviously, many modifications and variations are possible in view of the above teachings. These embodiments best illustrate the principles of the invention and its practical applications, so that those skilled in the art can make the invention and various modifications while making various modifications to suit the particular intended use. In order to make the best use of the embodiments, they have been shown and described. It is intended that the scope of the invention be defined by the appended claims and their equivalents.

Claims (15)

A monolithic surface emitting laser array,
A reflective layer;
A light emitting layer (102);
A diffraction grating layer (112) configured using two or more non-periodic subwavelength diffraction gratings, and each diffraction grating is configured to form a cavity resonator with the reflector, A diffraction grating is a monolithic surface emitting laser that is configured with a diffraction grating pattern that realizes one or more internal resonator modes and that realizes one or more external transverse modes emitted through the diffraction grating. array. A substrate (106) disposed on the reflective layer;
A first electrode (108) disposed on the substrate;
A second electrode (114) disposed on the diffraction grating layer, wherein the second electrode is configured to have two or more openings, each opening having the two or more sub-wavelengths; The laser array of claim 1, further comprising: a second electrode (114) configured to expose one of the diffraction gratings.   The laser array of claim 1, wherein the reflective layer further comprises a distributed Bragg reflector (104).   The reflective layer further includes a second diffraction grating layer (1602) configured using two or more non-periodic subwavelength diffraction gratings (1604), The laser array of claim 1, wherein each subwavelength diffraction grating is aligned with one subwavelength diffraction grating or the two or more subwavelength diffraction gratings in the diffraction grating layer.   The laser array according to claim 1 or 4, wherein the diffraction grating pattern further comprises a one-dimensional pattern of lines separated by grooves (300).   The laser array according to claim 1, wherein the diffraction grating pattern comprises a two-dimensional diffraction grating pattern.   Each sub-wavelength diffraction grating further comprises a film (132, 133) supported in a floating state, forming a gap (216, 217) between the sub-wavelength diffraction grating and the light emitting layer. The laser array described in 1.   The sub-wavelength diffraction grating further comprising an insulating layer (110) disposed between the light emitting layer and the diffraction grating layer, for confining current and optically confining light emitted from the light emitting layer; The laser array of claim 1, comprising two or more openings (126-128) to be aligned.   The laser array according to claim 1, wherein the light amplified in each cavity and emitted from the cavity is polarized or not polarized based on the grating pattern of each corresponding subwavelength grating. .   The laser array of claim 1, wherein two or more sub-wavelength diffraction gratings of the diffraction grating layer are configured to form a single mode cavity for emitting single mode light. Each of the sub-wavelength diffraction gratings configured with a diffraction grating pattern that implements one or more internal resonator modes further comprises a diffraction grating pattern that results in a light beam having a donut-shaped luminance cross section. 2. The laser array according to 1.   The laser array of claim 1, wherein one or more of the sub-wavelength diffraction gratings can be configured to form a hemispherical resonator (1302) that uses the reflector. A laser system (1700) comprising:
A monolithic surface emitting laser array (1701) comprising two or more surface emitting layers configured according to claim 1;
A multi-waveguide fiber (1710), each waveguide being coupled to the corresponding waveguide and propagating through the waveguide, wherein each waveguide is coupled to the laser array. A laser system aligned with a surface emitting laser.   The multi-waveguide fiber further comprises a photonic crystal fiber (1710) configured to have a plurality of cores (1714), each core aligned with a surface emitting laser of the laser array. The laser system described in 1.   The laser system of claim 13, wherein the multi-waveguide fiber further comprises a group of hollow waveguides, each hollow waveguide being aligned with a surface emitting laser of the laser array.

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